1. Field of the Invention
This invention relates generally to an apparatus and a method for controlling power consumed by a passenger train, in particular to an apparatus and method of load shedding using a trainwide communication system whereby at least one train car in the passenger train receives power from a high voltage source and has an intermediate voltage power supply which outputs intermediate voltage to other cars on the train.
2. Background of the Related Art
Trains are typically powered from a high voltage (e.g., 600 V) DC power supplied by a high voltage line on a third rail. It is common that some cars on such trains carry intermediate voltage power supplies which convert the high level DC voltage to an intermediate level (e.g., 350 V) from which heating, air conditioning and braking units are driven. A single line running the length of the train can be connected to these power supplies and consequently, every car does not have to carry such a power supply.
Each car carrying such an intermediate voltage power supply is coupled to the high voltage 600 V line. However, since the high voltage power is supplied by separate high voltage sources, there are often gaps along the third rail at which no high voltage power is available. Consequently, if the train happens to stop so that a car carrying one of the intermediate voltage power supplies is at one of these gaps, or if one or more of the intermediate voltage power supplies breaks down, a fewer number of intermediate voltage power supplies must supply power to the same number of heating, air conditioning and braking units. This can result in overloading the intermediate voltage power supplies and/or damaging the heating, air conditioning and braking units (the latter possibly resulting in brake failure).
In addition, other equipment on the cars such as lighting circuitry or door control circuitry require even lower (e.g., 37 V) operating voltages. Such operating voltages can typically be obtained by using a converter which can be placed on each car of the train connected to the high voltage (600 V) line and a storage battery. The converter unit charges the storage battery which is coupled to a low voltage (37 V) line that also runs along the entire train. Again, if the train stops at gaps along the high voltage line, the converter cannot receive the high voltage it needs to charge the battery. Consequently, fewer converters and batteries must drive the same number of lighting and door units.
With the advent of trainwide communication systems, a solution to the above problems has become possible. For example, a train communication system is being developed by the assignee of the present application which, based on the proposed European specification DIN 43322 for "Serial Interfaces to Programmable Electronic Equipment for Rail Vehicles," incorporated herein by reference, enables a master node located typically in a head car of a train to communicate via a serial bus to slave nodes on middle cars of the train and on a tail car of the train. See also, "International Standard-Information processing systems-Data communication-High-level data link control elements of procedures, ISO 4335", Third edition, Global Engineering Documents, Irvine, CA, 1987, the subject matter of which is also incorporated herein by reference.